#include <stdio.h>
#include <math.h>
int main()
{
	float x1 = 0, x2 = 0, y1 = 0, y2 = 0;
	scanf("%f %f %f %f", &x1, &y1, &x2, &y2);
	float d = (x2-x1) * (x2-x1);
	d += (y2-y1) * (y2-y1);
	d = sqrt(d);
	printf("%.2f", d);
	return 0;
} 
